1. Field of the Invention
The present invention relates to an error signal generator, and more specifically to an error signal generator for producing on the basis of digital data processing a plurality of error signals which can be used to control frequencies and/or phases of various periodical operations.
2. Description of the Related Art
Conventionally, various types of devices have been used for generating an error signal which is used to control a control value to a target or desired value. Recently, such error signal generating devices tend to be digitized and assembled in the form of an integrated circuit for increased performance and no adjustment.
At present, on the other hand, such error signal generating devices are widely used in video tape recorders for control of the phase and the revolution speed of associated motors. In general, the video tape recorder comprises a so-called cylinder motor for driving a rotary head and a so-called capstan motor for tape transport. The phase and revolution speed of these motors have to be controlled at various values determined in accordance with selected operation modes of the video tape recorder. For example, the phase of the capstan motor is controlled on the basis of the 1/2 frequency-divided pulse of the vertical synchronizing pulse at the time of reproduction, and in the recording condition on the basis of the vertical synchronizing pulse obtained by frequency division of the color subcarrier.
In brief, to detect the phase and the revolution speed, ordinarily, each motor is associated with a pulse generator adapted to generate one pulse per revolution for detection of revolution speed and another pulse generator adapted to generate a pulse when the motor assumes a predetermined phase. The period of the speed detection pulse thus obtained is compared in a digital manner with a target period determined by the selected operation mode so as to produce a speed error signal. The phase detection pulse is compared with a phase reference pulse, and the phase difference is also compared in a digital manner with a target phase difference given in accordance with the selected operation mode.
As mentioned above, the video tape recorder is required to produce the phase error signal and the speed error signal for each of the cylinder motor and the capstan motor. Therefore, the video tape recorder has to provide four error signal generation functions. In conventional recorders, the four error signal generation functions have been performed by four discrete digital units in a parallel processing manner.
However, the provision of the four error signal generation units will make the overall circuit large, which means that a large chip area is required when it is assembled in a large scaled integrated circuit. This problem is significant in a handy type video tape recorder.